1. Field of the Invention
The present invention relates to a hydraulic press and particularly relates to a hydraulic press suited for sheet metal formation.
2. Description of the Related Art
To manufacture the door, food, trunk lid or the like of a vehicle, hem-press for peening an inner component and an outer component at their edges is conducted. To this end, a hydraulic press is employed. According to a conventional hydraulic press, a hydraulic pump is constantly driven by an induction motor. If no oil is supplied to a hydraulic cylinder, pressure oil is returned to a tank by an unload valve. This causes the temperature rise of the oil, requires a water-cooling cooler or the like which water-cools the hydraulic oil and consumes lots of energy (power).
The conventional hydraulic press has the following disadvantage. If a single hydraulic cylinder is employed, pressure oil in large quantities and much time are required to elevate dies, with the result that productivity deteriorates. To solve this disadvantage, there is proposed in JP-A-2000-254799 (to be referred to as xe2x80x9cReference 1xe2x80x9d hereinafter) that a screw sliding driver 15 and a hydraulic cylinder sliding driver 22 are disposed in parallel, the screw sliding driver 15 is employed for fast elevation and the hydraulic cylinder sliding driver 22 is employed only to pressurize a workpiece. In addition, there is proposed in JP-A-10-263888 (to be referred to as xe2x80x9cReference 2xe2x80x9d hereinafter) that a high speed cylinder 36 for elevation and a pressure cylinder 37 for pressurizing a workpiece are employed. Further, there is proposed in JP-A-10-180499 (to be referred to as xe2x80x9cReference 3xe2x80x9d hereinafter) that a first cylinder 24 for pressurizing a workpiece, a second cylinder 25 for descending the workpiece and a third cylinder 26 for ascending the workpiece are provided and a hydraulic pump 17 is driven by an alternating current servo motor 18, thereby accurately controlling a ram 6.
Nevertheless, according to Reference 1, since the screw sliding driver 15 and the hydraulic cylinder sliding driver 22 are provided, the structure of this hydraulic press and control over the hydraulic press are disadvantageously complicated. According to Reference 2, since the two cylinders 36 and 37 are connected in series and have large heights, the hydraulic press becomes disadvantageously large in size. Further, according to Reference 2, since a servo valve 52 is employed to adjust the pressure and quantity of oil, the hydraulic press has disadvantageously heavy energy loss. According to Reference 3, although the alternating current servo motor 18 is employed, the hydraulic pump 17 connected to the motor 18 discharges oil in one direction but cannot discharge oil in a counter direction. Due to this, the alternating current servo motor 18 controls only the number of revolutions and torque of the pump 17 and not control the pump 17 to make a counter rotation. As a result, return oil from the respective cylinders 24, 25 and 26 is returned to the tank 16, in which tank energy loss and the temperature rise of the oil disadvantageously occur.
It is, therefore, an object of the present invention to provide a hydraulic press which has the smaller temperature rise of hydraulic oil, which can dispense with a water-cooling cooler or the like, which can be made compact in size and which can realize energy saving.
In order to achieve the above mentioned object, a hydraulic press according to the present invention as shown in FIG. 2 is characterized by comprising:
a multi-cylinder including a first cylinder chamber 51 having a small pressure receiving area and used for reciprocation, a second cylinder chamber 52 having an equal pressure receiving area to the pressure receiving area of the first cylinder chamber 51, a third cylinder chamber 53 having a large pressure receiving area and used for reciprocation, and an integral piston member 54 partitioning the respective cylinder chambers 50;
a constant volume, reversible hydraulic pump 7, and a servo motor 6, driving the hydraulic pump 7 to rotate in positive and counter directions;
a closed hydraulic circuit 31 and 34 connecting said first cylinder chamber 51 to said second cylinder chamber 52 through said hydraulic pump 7;
an automatic supply hydraulic circuit 32 connecting said third cylinder chamber 53 to an oil tank 1 through said automatic supply valve 23;
a pressurization hydraulic circuit 35 connecting one of discharge ports of said hydraulic pump 7 to the third cylinder chamber 53 through a check valve 27;
a pressure sensor 28 detecting oil pressure of said third cylinder chamber 53; and
a controller 80 controlling said servo motor 6 based on a signal from said pressure sensor 28.
According to the present invention, a first cylinder chamber 51 is employed as a quick feed and pressurization cylinder, a second cylinder chamber 52 is employed as a quick return cylinder and a third cylinder chamber 53 is employed as a pressurization cylinder. During quick feed, a closed hydraulic circuit which ranges from the second cylinder chamber 52 to the first cylinder chamber 51 through a hydraulic circuit 31, a hydraulic pump 7 and a hydraulic circuit 34 is formed. Since the pressure receiving area of the first cylinder chamber 51 is set equal to that of the second cylinder chamber 52, the quantity of hydraulic oil discharged from the second cylinder chamber 52 is equal to that supplied to the first cylinder chamber 51. Due to this, the hydraulic oil discharged from the hydraulic pump 7 is only passed through the closed hydraulic circuit comprising the second cylinder chamber 52, the hydraulic circuit 31, the hydraulic pump 7, the hydraulic circuit 34 and the first cylinder 51 and not returned to an oil tank 1. Accordingly, no energy loss and no temperature rise of the hydraulic oil occur. It is noted that the hydraulic oil of the oil tank 1 is sucked to the pressurization third cylinder chamber 53 through an automatic supply hydraulic circuit 32 and an automatic supply valve 23 by negative pressure.
Likewise, during quick return, a closed hydraulic circuit which ranges from the first cylinder chamber 51 to the second cylinder chamber 52 through the hydraulic circuit 34, the hydraulic pump 7 and the hydraulic circuit 31 is formed. By driving the hydraulic pump 7 to rotate in a counter direction, the hydraulic oil is fed from the first cylinder chamber 51 to the second cylinder chamber 52 to thereby regress a piston member 54. As in the case of the quick feed, no energy loss and no temperature rise of the hydraulic oil occur. It is noted that the hydraulic oil of the third cylinder chamber 53 is relieved to the oil tank 1 through the automatic supply valve 23 and the automatic supply hydraulic circuit 32. In this way, during the quick feed and quick return, the hydraulic oil is automatically sucked and discharged to and from the third cylinder chamber 53, thereby decreasing the discharge quantity of the hydraulic pump 7 and making the hydraulic pump 7 small in size.
When pressure is applied, the automatic supply valve 23 is closed. In addition, the hydraulic circuit 34 which communicates with the hydraulic pump 7 is connected to the pressurization hydraulic circuit 35 which communicates with the third cylinder chamber 53. By driving the hydraulic pump 7 to rotate in a positive direction, the hydraulic oil is fed to the third cylinder chamber 53 and the first cylinder chamber 51 and the piston member 54 is pressed out with pressure received by a pressure receiving area which is a combination of the pressure receiving area of the third cylinder chamber 53 and that of the first cylinder chamber 51. At this moment, the oil pressure of the third cylinder chamber 53 is detected by a pressure sensor 28 and the number of revolutions of the servo motor 6 is controlled so as to provide appropriate pressure. In this way, the oil pressure is controlled not by a servo valve but by a servo motor 6, i.e., controlled according to the number of revolutions and torque of the hydraulic pump 7. Therefore, energy loss is small and the temperature rise of the hydraulic oil is small. Moreover, a change in the tact system of the hydraulic press such as a change in press pressure according to a workpiece can be easily made by only electrically changing settings in a controller 80 and changing control over the number of revolutions of the servo motor 6 and the like.
In a standby state, the servo motor 6 and the hydraulic pump 7 stop and pressure oil is not relieved from an unload valve. Therefore, no energy loss and no temperature rise of the hydraulic oil occur. As can be seen, in the hydraulic press of the present invention, the temperature rise of the hydraulic oil hardly occurs and it is unnecessary to provide a cooling unit. The present invention exhibits an advantage in that a hydraulic press which contributes to energy saving and which is compact in size can be provided.
According to the present invention, the constant volume reversible hydraulic pump 7 can be a vane pump.
If so, the vane pump has less pulsation of discharge pressure. Therefore, noise is decreased and press pressurization force is stabilized.
According to the present invention, the constant volume, reversible hydraulic pump 7 can be a piston pump.
If so, the piston pump can obtain a discharge quantity with less error, high speed rotation and high pressure. Therefore, it is possible to realize a high speed, high pressure hydraulic press by using a small-sized-cylinder.
According to the present invention, as shown in FIG. 1, the hydraulic press according to the present invention is characterized in that
said controller 80 comprises means for controlling said servo motor 6 based on a signal from a position sensor 91 detecting a position of said piston member 54 or a position of a ram 205, a slider 204 or the like integral with the piston member 54.
By thus forming the hydraulic press, it is possible to accurately control a location and the like for changing the piston member 54 from high speed movement to low speed, high pressure movement. It is also possible easily change the tact system of the hydraulic press by changing settings in the controller 80.
According to the present invention, as shown FIG. 5, the hydraulic press according to the present invention is characterized in that said controller 80 comprises:
a rotation detector 92 detecting rotation of said servo motor 6; means for storing a total number of revolutions of said servo motor 6 based on output of the rotation detector 92; and means for specifying a position of a ram 205 or a slider 204 from the stored total number of revolutions, and for controlling said servo motor 6 based the specified position of the ram 205 or the slider 204.
By so forming, the closed hydraulic circuit which ranges from the second cylinder chamber 52 to the first cylinder chamber 51 through the hydraulic circuit 31, the hydraulic pump 7 and the hydraulic circuit 34 is formed. Since the hydraulic pump 7 is a constant volume, reversible hydraulic pump, the total number of revolutions of the servo motor 6 (the number of revolutions thereof in counter direction is counted as negative), i.e., the total number of revolutions of the hydraulic pump 7 corresponds to the volume of the hydraulic oil discharged to either the cylinder chamber 51 or 52. It is, therefore, possible to specify the position of the piston member 54 from the total number of revolutions and to accurately control the location at which the piston member 54 changes from the high speed movement to the low speed, high pressure movement. Further, it is possible to easily change the tact system of the hydraulic press by changing settings in the controller 80. Besides, since a detector 92 is attached to the servo motor 6, a wiring can be easily arranged.